【導讀】數字信號處理是最強大的技術，將塑造二十一世紀的科學與工程之一。上述各領域已建立了深厚的DSP技術，用自己的算法，數。DSP教育包含兩個任務：學習一般適用于作為一個整體領。本章開始描述DSP已在幾個。不同領域的戲劇性效果的數字信號處理的世界，我們的旅程。DSP回答了這個問題：下一步怎么辦？DSP的根是在20世紀60年代和70年代數字計算機時首次面世。昂貴的，在這個時代，DSP是有限的，只有少數關鍵應用。的個人電腦革命，引起新的應用DSP的爆炸。DSP的突然被帶動的商業(yè)市場。DSP的市民等產品達到：移動電話機，光盤播放器，十年后，DSP已成為標準的本科課程的一部分。天，DSP是一種在許多領域的科學家和工程師所需要的基本技能。DSP的文獻多是令人費解，甚至在該領域經驗豐富的。本章的其余部分說明，其中DSP已經產生了革命性的變化的地區(qū)。DSP已徹底改變電信業(yè)在許多。DSP可以在組合提供幾個重要的功能，包括：過濾，加法和減法信

　　

【正文】 reas, all of which relate to this basic problem. First, DSP can press the pulse after it is received, providing better distance determination without reducing the operating range. Second, DSP can filter the received signal to decrease the noise. This increases the range, without degrading the distance determination. Third, DSP enables the rapid selection and generation of different pulse shapes and lengths. Among other things, this allows the pulse to be optimized for a particular detection problem. Now the impressive part: much of this is done at a sampling rate parable to the radio frequency used, as high as several hundred megahertz! When it es to radar, DSP is as much about highspeed hardware design as it is about algorithms. Sonar Sonar is an acronym for Sound Navigation and Ranging. It is divided into two categories, active and passive. In active sonar, sound pulses between 2 kHz and 40 kHz are transmitted into the water, and the resulting echoes detected and analyzed. Uses of active sonar include: detection amp。 localization of undersea bodies, navigation, munication, and mapping the sea floor. A maximum operating range of 10 to 100 kilometers is typical. In parison, passive sonar simply listens to underwater sounds, which includes: natural turbulence, marine life, and mechanical sounds from submarines and surface vessels. Since passive sonar emits no energy, it is ideal for covert operations. You want to detect the other guy, without him detecting you. The most important application of passive sonar is in military surveillance systems that detect and track submarines. Passive sonar typically uses lower frequencies than active sonar because they propagate through the water with less absorption. Detection ranges can be thousands of kilometers. DSP has revolutionized sonar in many of the same areas as radar: pulse generation, pulse pression, and filtering of detected signals. In one view, sonar is simpler than radar because of the lower frequencies involved. In another view, sonar is more difficult than radar because the environment is much less uniform and stable. Sonar systems usually employ extensive arrays of transmitting and receiving elements, rather than just a single channel. By properly controlling and mixing the signals in these many elements, the sonar system can steer the emitted pulse to the desired location and determine the direction that echoes are received from. To handle these multiple channels, sonar systems require the same massive DSP puting power as radar. Reflection seismology As early as the 1920s, geophysicists discovered that the structure of the earth39。s crust could be probed with sound. Prospectors could set off an explosion and record the echoes from boundary layers more than ten kilometers below the surface. These echo seismograms were interpreted by the raw eye to map the subsurface structure. The reflection seismic method rapidly became the primary method for locating petroleum and mineral deposits, and remains so today. In the ideal case, a sound pulse sent into the ground produces a single echo for each boundary layer the pulse passes through. Unfortunately, the situation is not usually this simple. Each echo returning to the surface must pass through all the other boundary layers above where it originated. This can result in the echo bouncing between layers, giving rise to echoes of echoes being detected at the surface. These secondary echoes can make the detected signal very plicated and difficult to interpret. Digital Signal Processing has been widely used since the 1960s to isolate the primary from the secondary echoes in reflection seismograms. How did the early geophysicists manage without DSP? The answer is simple: they looked in easy places, where multiple reflections were minimized. DSP allows oil to be found in difficult locations, such as under the ocean. Image Processing Images are signals with special characteristics. First, they are a measure of a parameter over space (distance), while most signals are a measure of a parameter over time. Second, they contain a great deal of information. For example, more than 10 megabytes can be required to store one second of television video. This is more than a thousand times greater than for a similar length voice signal. Third, the final judge of quality is often a subjective human evaluation, rather than an objective criterion. These special characteristics have made image processing a distinct subgroup within DSP. Medical In 1895, Wilhelm Conrad R246。ntgen discovered that xrays could pass through substantial amounts of matter. Medicine was revolutionized by the ability to look inside the living human body. Medical xray systems spread throughout the world in only a few years. In spite of its obvious success, medical xray imaging was limited by four problems until DSP and related techniques came along in the 1970s. First, overlapping structures in the body can hide behind each other. For example, portions of the heart might not be visible behind the ribs. Second, it is not always possible to distinguish between similar tissues. For example, it may be able to separate bone from soft tissue, but not distinguish a tumor from the liver. Third, xray images show anatomy, the body39。s structure, and not physiology, the body39。s operation. The xray image of a living person looks exactly like the xray image of a dead one! Fourth, xray exposure can cause cancer, requiring it to be used sparingly and only with proper justification. The problem of overlapping structures was solved in 1971 with the introduction of the first puted tomography scanner (formerly called puted axial tomography, or CAT scanner). Computed tomography (CT) is a classic example of Digital Signal Processing. Xrays from many directions are passed through the section of the pati